1. Field of the Invention
The present invention relates to power amplification circuits preferably for use in power amplification modules that amplify signals of a plurality of frequency bands.
2. Description of the Related Art
In general, known wireless communication devices, such as cellular phones, are equipped with a transmission device for transmitting a plurality of transmission signals. A transmission device 102 described in Japanese Unexamined Patent Application Publication No. 2008-154201 and illustrated in FIG. 5 is used as such a transmission device of a multiband wireless communication device. A power amplification module 104 is used in the transmission device 102 and a power amplification circuit 110 of the power amplification module 104 has the following configuration.
The power amplification circuit 110 employs a power amplifier 109, a power detector 119, an isolator 121 and so forth for both first and second transmission signals and the two types of signal are separated by a switch 122 on the output side.
In such a power amplification circuit 110, the switch 122 is incorporated into a main line through which a transmission signal passes and as a result the following problems and issues arise. That is, power loss occurs in the switch 122, distortion occurs due to the large amount of power entering the switch 122 and the switch is required to have a high electrical power handling capability.